In Joss Whedon's "Serenity," set 500 years in the future, Capt. Malcolm "Mal" Reynolds (Nathan Fillion) and his mercenary crew ride a rust-bucket spaceship, the Serenity, custom-built for rapid getaways. These contraband wheeler-dealers are ready for rough ridin', wearing cowboy boots, six-gun holsters and bandoleers. Half a millennium after Neil Armstrong's one small step for mankind and we're back in the saddle again.

Not surprisingly, Mal and company have their enemies. There are the Alliance goons, soldiers of the Big Brotherly federation that rules the solar system. They've been hunting Mal and his rebel-yellers ever since the civil war -- which Mal's side lost. Then there are the flesh-eating Reavers. You don't want to dawdle when those guys show up hungry.

Fans of "Firefly," the fabulous but short-lived TV show that spawned this movie, mourned when the 2002 series was canceled after only 12 weeks. But in the now traditional kabuki of fan power, their enthusiastic snapping up of the show's DVDs prompted Universal to pony up $50 million for the big-screen version. They'll be thrilled at this reunion of endearing rogues.

It should be stressed right away, "Serenity" isn't just for the "Firefly" set. Writer-director Whedon -- who meteor-showered Planet Earth with "Buffy the Vampire Slayer" and "Angel" -- is a pop culture ringmaster whose bullwhip dialogue, flamboyant characters and narrative genius can make an exhilarating three-ring show out of anything.

"Serenity" proves that conclusively. Sure, in the retelling, Whedon has had to boil off a lot of the complexity of the series. But the enjoyable result is a highly concentrated, amphetamine-fueled reprise, designed to give fans a sentimental jolt and boost new devotees. If newcomers feel overwhelmed by the fast-moving details, they'll be drawn back in by the otherworldly mayhem.

"We might experience some turbulence," Mal announces matter-of-factly into the Serenity intercom, as the ship endures yet another attack. "And then explode."

"I don't want to explode," says crew member Jayne (Adam Baldwin), as if, in this loco universe, someone might consider the other option.

When Mal provides passage for a tight-lipped, nervy doctor and his seemingly catatonic sister, River Tam (Summer Glau), a new hell is set to yawn open. River is a 17-year-old psychic whose powers to understand the deepest secrets of the Alliance put her (and the Serenity crew) at massive risk. That's where a ruthless Alliance assassin named the Operative (smooth 'n' cool Chiwetel Ejiofor) comes in. Most of the crew would sell their mothers to Reavers for a small bag of gold, but they decide to protect River -- on rebel principle.

That turns out to be a mistake. River gives new meaning to the term "problem passenger." Suffering mental damage from the gruesome mind experiments the Alliance subjected her to, she's a 90-pound time bomb with kung fu skills. In her bouts of manic wigginess, she doesn't always differentiate between friend and foe.

"She's starting to damage my calm," says Jayne, after suffering a River special in his nether regions.

"Serenity" may be little more than an ultra-sophisticated chase movie, with a big showdown at the communications pad of Mr. Universe (David Krumholtz), who functions as a sort of Richie Rich with his all-news space station. But the real joy comes from the dysfunctional rebel family, whether it's the screwball tension between Mal and love interest Inara Serra (Morena Baccarin), the ship's courtesan, who plies her trade to passengers, much to Mal's chagrin; or the dime-novelly language of Jayne as he says of the Reavers: "Eating people alive -- where does that get fun?"

They're a futuristic King Arthur's round table, or Dirty Dozen, or Robin Hood and his Merry Men; heck, they're even "Seinfeld." And no matter what's coming their way, post-apocalyptic doom or gloom, this James Gang of the galaxy is just plain fun to watch.

Serenity (119 minutes at area theaters) is rated PG-13 for violence, profanity and sexual themes.